1. Field of the Invention
The present invention relates to an elastic wave device that includes a piezoelectric substrate with a thickness equal to or less than a wavelength of a propagating elastic wave.
2. Description of the Related Art
Various elastic wave devices using a plate wave, such as a Lamb wave, have been proposed. By providing an interdigital transducer (IDT) electrode on a thin piezoelectric substrate, various elastic wave characteristics can be obtained using a plate wave. For example, Japanese Patent No. 4613960 describes a technique in which, by using the A1 mode, elastic wave characteristics of a high acoustic velocity of 10000 m/second or more can be achieved.
Japanese Unexamined Patent Application Publication No. 2002-152007 discloses an elastic wave device using the SH mode of a plate wave. Japanese Unexamined Patent Application Publication No. 2002-152007 states that wide-band characteristics can be achieved using the SH mode.
However, a conventional elastic wave device using a plate wave has a problem in that characteristics change significantly with changes in the thickness of the piezoelectric substrate or the electrode. Specifically, an electromechanical coupling coefficient (i.e., a bandwidth, an acoustic velocity, and a stop band) tends to change significantly when the thickness of the piezoelectric substrate or the electrode changes. This means that it has been difficult to stably manufacture elastic wave devices having desired characteristics.
To achieve a wide bandwidth, it is necessary to reduce the duty or the thickness of the IDT electrode. In this case, the effect of resistance loss of the electrode increases in a high frequency band, such as a GHz band. Therefore, the elastic wave device formed as a resonator has a problem of increased resonant resistance, and the elastic wave device formed as a filter has a problem of increased loss.